The present invention relates in general to netted communication systems and in particular to netted radio broadcast communications.
Radio communication systems rely on modulating carrier frequencies (i.e. a channel) in a finite portion of the electromagnetic spectrum to wirelessly transmit and receive signals. Modulation can be performed on the amplitude, frequency, and/or phase of the carrier frequency to separate the signal from unwanted noise. The signals typically convey information such as voice, video, and computer data between transmitting/receiving devices such as voice terminals (e.g., wireless phone) and data terminals (e.g., portable computer).
In order to transmit the signals over a large distance, a relay such as a satellite may be used. Passive communication satellites may be used to return transmitted signals to earth on the same carrier frequency they were transmitted on. Active communication satellites can be used to receive the transmitted signals on one carrier frequency and to retransmit the signals on another carrier frequency. Geosynchronous satellites are especially well suited for such a task due to their stationary position relative to the earth""s surface.
Often it is desirable to communicate in a netted broadcast fashion. For example, a military commander may need to transmit an order to a large number of receivers which individually confirm that they received the order, or a data server may need to transmit information to multiple clients who verify reception. Currently, systems relay broadcast signals on a particular frequency and people who want to participate, tune their receiver to that channel, as in a UHF satellite system. Alternatively, conference calls may be established. Each participant in the conference call communicates with a central station such as a cell site or satellite using a pair of unique carrier frequencies. The central station combines the signals of conferencing callers and then transmits the. combined signal to each receiver using its unique carrier frequency.
Prior art approaches for netted broadcast communication suffer from certain drawbacks. For instance, conference calling requires one channel per user. As the number of receivers grows the channels are exhausted. Therefore, only a relatively small number of receivers may participate. Similarly, UHF and other broad beam systems have a relatively small number of channels and require users to tune their receiver to one particular channel. None of these techniques are well suited for use in a digital beam forming satellite communication system, wherein multiple beams distinguished by frequency band are used to cover multiple geographical regions while reusing frequencies to increase capacity in a spectrum limited system.
The present invention relates to efficient bandwidth utilization in radio communication systems broadcasting to a plurality of receivers in distinct geographical regions representing multiple nets and multiple conflict regions. This invention may support a standalone system, but it also may serve as an overlay on an existing system that offers point-to-point communications, retaining protocols, channels, etc. of the latter. The present invention describes a system and method for distributing the radio signals wherein transmitting devices transmit signals to relay devices which, in turn, retransmit the signals on supplementary carrier frequencies to a large number of users distributed across a large geographical region (i.e., multiple beams, multiple conflict regions, and multiple nets). The signals are then recovered by receiving devices preferably in one or more beams of a beam forming satellite. Preferably, only one frequency channel per beam is used for traffic from a particular broadcast, thereby increasing the broadcast capacity and allowing an unlimited number of receivers. Bandwidth can be dynamically allocated to broadcast service, or it can be returned to be used for baseline (existing) services, e.g., point-to-point (ptp), voice, data, fax services.
The present invention utilizes existing protocols and control channels to configure and set up voice net broadcast services with little to no modifications to control channels. The present invention will support simultaneous point-to-point features (voice, data, and fax) while supporting voice broadcast services. The capacity of the system is limited only by the amount of available power and bandwidth. Control channels are used for registration, net set-ups, authentication, and net key transmission, while traffic channels are used for the actual signal transmission. In addition, a separate control channel is associated to each net for link maintenance purposes (e.g., time, frequency, and power control).
In accordance with a first aspect of the invention, a system for broadcasting netted radio signals is provided. The system comprises a first transmitting device for transmitting a first signal on a first carrier frequency. The system also comprises a relay device for receiving the first signal on the first carrier frequency and transmitting the first signal on second and third carrier frequencies. In addition, the system is provided with a first receiving device for receiving the first signal on the second carrier frequency and a second receiving device for receiving the first signal on the third carrier frequency.
In a preferred embodiment, the relay device comprises a satellite device. In such an embodiment the relay device may be a digital beam forming geosynchronous communications satellite. In another preferred embodiment, the relay device comprises a satellite and a ground segment.
In any of the forgoing embodiments, the signals may comprise voice signals and/or digital signals. Further, any transmitting device may comprise a portable voice communicator and/or a data terminal. Still further, the transmitting devices, relay device, and/or receiving devices may comprise time division, code division, and/or frequency division multiple access devices. The transmitting devices (terminals) can support all existing voice/data/fax services while offering net broadcast features. In addition, any of the participating users may be able to transmit in the net. The control mechanism for getting access to the net is managed by push-to-talk access method. Precedence and preemption capability is also implanted to provide access and transmission privileges to users with higher authority. In some preferred embodiments, the transmitting device and/or receiving device may be coupled to a communications network. In such an embodiment, the communications network may comprise a public switched telephone network and/or the Internet. Further in any of the forgoing embodiments, the carrier frequency may be an L-band, S-band, C-band, Ku-band and/or a Ka-band frequency.
In accordance with another aspect of the invention, a method of broadcasting a netted radio signal is provided. The method comprises the steps of transmitting a first message requesting participation in a predetermined distribution of the radio signal and receiving a second control message granting permission and acknowledging participation in the predetermined distribution of the radio signal (on existing control channels) and identifying a frequency on which to transmit and/or receive the radio signal. The method further comprises the steps completing authentication, and ciphering process and granting net session key for privacy and of tuning a receiver to the identified frequency and receiving the radio signal on the identified frequency. Upon completion of this step, the users may select to tune to assigned receiver frequencies to receive broadcast satellite. In addition, users may tune to another frequency when they wish to transmit on the net.
In a preferred embodiment, the first message is transmitted by a voice terminal or a data terminal. In some preferred embodiments, the relay device comprises a satellite device. In such an embodiment, the relay device may be a digital beam forming geosynchronous communications satellite. In another preferred embodiment, the relay device comprises a ground station. In yet another preferred embodiment, the second message identifies an L-band, S-band, C-band, Ku-band and/or a Ka-band frequency. In any of the forgoing embodiments, the signals may comprise voice signals and/or a digital signals.
In accordance with yet another aspect of the invention, a method of broadcasting a radio signal is provided. The method comprises the steps of transmitting a first message, e.g., (PTT), requesting participation in a predetermined distribution of the radio signal and determining a frequency on which to transmit the radio signal based on previous assignment of frequencies for specific nets. The method further comprises the step of transmitting a second message acknowledging participation in the predetermined distribution of the radio signal and acknowledging a preselected frequency on which the radio signal is to be transmitted. In addition the method comprises the step of transmitting the radio signal On the identified frequency.
In a preferred embodiment, the first message is transmitted by a voice terminal or a data terminal. In some preferred embodiments, the relay device comprises a satellite device. In such an embodiment the relay device may be a digital beam forming geosynchronous communications satellite. In another preferred embodiment, the relay device comprises a ground station. In yet another preferred embodiment, the second message identifies an L-band, S-band, C-band, Ku-band and/or a Ka-band frequency. In any of the forgoing embodiments, the signals may comprise voice signals and/or digital signals.
The present invention significantly increases the capacity of broadcast radio communication systems by using one frequency channel per beam per broadcast. A large number of multiple broadcasts and networks, each covering distinct and (possibly) overlapping geographical regions, may be formed with virtually an unlimited number of transceivers participating. Further, the techniques of the present invention in no way preclude resource sharing with conventional (non-netted broadcast) traffic at the relay.